Method for purifying (meth)acrylic acid

Abstract

A method for purifying a crude (meth)acrylic acid obtained by a vapor phase catalytic oxidation method, characterized in that the crude (meth)acrylic acid having most parts of water and acetic acid removed therefrom, is fed to and distilled in a first distillation column of a purification system comprising first to third three distillation columns, the top fraction from the first distillation column is fed to and distilled in the second distillation column, the resulting top fraction is recovered as a high purity (meth)acrylic acid product, the bottoms from the first and second distillation columns are fed to and distilled in the third distillation column, and the resulting top fraction is fed to the first distillation column.

1 - 21 . (canceled)  
     
     
         22 . A method for purifying (meth)acrylic acid, which comprises distilling and purifying acrylic acid or methacrylic acid obtained by a vapor phase catalytic oxidation method (hereinafter referred to as a crude (meth)acrylic acid), characterized in that the distillation is carried out at a bottom temperature of not higher than 110° C. in the presence of a polymerization inhibitor comprising copper (meth)acrylate and/or copper dithiocarbamate, and a hydrazine compound.  
     
     
         23 . The method according to  claim 22 , wherein the copper (meth)acrylate is mixed to the crude (meth)acrylic acid and/or the top liquid.  
     
     
         24 . The method according to  claim 22 , wherein the copper dithiocarbamate is mixed to the crude (meth)acrylic acid and/or the top liquid.  
     
     
         25 . The method according to  claim 22 , wherein the copper (meth)acrylate is a solution obtained by dissolving at least one compound selected from copper powder, cupric carbonate, cuprous hydroxide, cupric hydroxide and copper acetate, in acrylic acid.  
     
     
         26 . The method according to  claim 22 , wherein the copper dithiocarbamate is copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate, copper dibutyldithiocarbamate, copper ethylenedithiocarbamate, copper tetramethylenedithiocarbamate, copper pentamethylenedithiocarbamate, copper hexamethylenedithiocarbamate or copper oxydiethylenedithiocarbamate.  
     
     
         27 . The method according to  claim 22 , wherein the hydrazine compound is hydrazine, hydrazine hydrate, phenyl hydrazine, hydrazine sulfate or hydrazine hydrochloride.  
     
     
         28 . The method according to  claim 22 , wherein the crude (meth)acrylic acid is distilled in the presence of a phenol compound.  
     
     
         29 . The method according to  claim 22 , wherein the crude (meth)acrylic acid is distilled in the presence of a phenothiazine compound.  
     
     
         30 . The method according to  claim 22 , wherein the distillation is carried out continuously by maintaining the temperature at a bottom temperature of at least 80° C.